In many fields it is desirable to provide assemblies which are able to decelerate, in a given, limited distance, an object which impacts the assembly. To do so, the assembly must absorb a significant percentage of the impact energy transferred by the object. In the past, this has been accomplished physically by providing the assembly with an energy absorbing member for supporting deformation of the assembly in order to absorb the energy of the impacting object. Alternative approaches are exemplified by commonly owned U.S. Pat. No. 5,700,545 and U.S. Ser. No. 09/018,666, filed on Feb. 4, 1998, which are incorporated herein by reference.
Within a vehicle, for example, occupants require protection from impact with interior components such as the pillars and headrails. These structures are typically made of steel tubing or steel channels which are welded together to form the structural cage or unitized body for the vehicle. Designers have attempted to place energy absorbers over the pillars, headrails and other parts of a vehicle to protect the vehicle occupants. Prior art approaches are found in the use of energy absorbing urethanes, rigid polymeric foams, blocks or cells or vanes of engineered plastics, various sheet metal configurations, metal beams, honeycombed metal, and other geometric solids. Most of these materials, however, while crushing generally absorb less than the desired amount of energy for a given displacement.
The desired response of an energy absorbing material from initial loading to failure is one wherein a near "square wave" response of force versus deflection is produced, such that the force exerted on the decelerated object is nearly unchanged over a desired range of crush distance or deflection. Commonly owned U.S. Pat. No. 5,700,545 issued to Audi et al. discloses such an energy absorbing structure, which is herein incorporated by reference. The energy absorbing member disclosed therein comprises an array of material, such as expanded metal, configured with vertical supporting faces which are generally orthogonal to spacing faces lying in the plane of an incident surface. While the energy absorption characteristics of such a structure are improved compared with those of the prior art, due to its configuration only the supporting faces, representing -50% of the absorbing member, are utilized in energy absorption. The spacing faces play little or no part in energy absorption since they generally lie in a plane orthogonal to the direction of impact.
Therefore, a need exists for an energy absorbing assembly which maximizes the use of energy absorbing members, so that maximum collapsible material is harnessed to produce superior energy absorbing characteristics and optimize the amount of energy absorbed per unit mass and per unit deflection of the energy absorbing member compared with prior art structures.
The amount of energy that is desired to be absorbed by the absorbing assembly depends on the kinetic energy of the object to be decelerated and the deflection of the background structure when impacted by the object. In the case of automotive interiors, the automobile body or cage deflects to a degree when impacted by occupants. The degree of deflection varies through the vehicle cage for a given amount of impact energy. So the energy absorbing structure is required to absorb different amounts of energy at different locations in the vehicle. The amount of crush space available also varies.
Thus, it would be desirable, additionally to provide a modular energy absorbing assembly wherein constituent modules offer different degrees of resistance to impact forces. Further, it would be useful to provide such a module wherein the material which supports each module is itself formed from an energy absorbing structure.